Progressive power lens, method of designing progressive power lens and method of evaluating progressive power lens

ABSTRACT

Improving the optical state of a progressive addition lens along a principal line of vision through which the line-of-sight of a wearer passes by making the displacement of a position at which an optical state becomes the best to be the same as the amount of inward movement of line-of-sight, when the wearer moves his line-of-sight from the front far distance to the front near distance. An expression OI&lt;DH may be satisfied to improve such an optical state of the progressive addition lens.

The present application is a divisional application of U.S. patentapplication Ser. No. 12/920,784, filed on Sep. 2, 2010, which is in turna National Stage entry of PCT/JP2009/066954, filed Sep. 29, 2009, thedisclosures of all of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a progressive-power lens (progressiveaddition lens) in which pupil diameter is taken into consideration,which is a kind of multifocal spectacle lens having addition power forcompensating for insufficient accommodation ability caused bypresbyopia, a method of designing the progressive addition lens, and amethod of evaluating the progressive addition lens.

BACKGROUND ART

A progressive addition lens is widely used in general due to itsadvantages such as that it is not easily recognized as a presbyopiaspectacle lens from appearance although it actually is, and that itallows a wearer to clearly look continuously from a far distance to anear distance without discontinuity.

However, it is difficult to design a progressive addition lens becauseit is necessary to arrange a plurality of visual fields within a limitedlens area without interposing a boundary between the plurality of visualfields, the plurality of visual fields being: a visual field for viewingfar distance, a visual field for viewing near distance, and a visualfield for viewing medium distance. For this reason, it is widely knownthat the progressive addition lens has its particular disadvantages suchas that each visual field is not always sufficiently wide, and thatthere is a region mainly in a side visual field which causes the wearerto feel distortion or sway of an image.

To overcome these disadvantages, many prior arts have been proposedsince long time ago. However, most of these prior arts are related todesign technique for obtaining more preferred power distribution orastigmatism distribution depending on individual prescribed power andwear state, and relatively few of these prior arts are made to improvebinocular vision of right and left eyes (see Patent Document 1 to 4).

Herein, the term “to improve binocular vision of right and left eyes”mainly means suitably arranging a near region and an intermediate regionto obtain good binocular near vision and binocular intermediate vision.

In the aforesaid prior arts, the art disclosed in Patent Document 1 is atechnique in which one sides of two kinds of lenses having bilaterallysymmetric design are replaced with each other to form a lens havingbilaterally asymmetric design, and the lens is rotated by about 10° dueto convergence of near vision and set into a frame so that theastigmatism distribution in horizontal direction is bilaterallysymmetrical. Further, the art disclosed in Patent Document 2 is atechnique relating to design of a progressive addition lens in which thenear vision region is bilaterally symmetric about the principal line ofvision. Further, the art disclosed in Patent Document 3 is a techniquerelating to design of a progressive addition lens in which theastigmatism distribution of the near vision region is bilaterallyasymmetric about the principal line of vision, in which the astigmatismdistribution is denser on the nose side and thinner on the ear side.Further, the art disclosed in Patent Document 4 is a technique relatingto a progressive addition lens in which the distortion of the nearvision region in vertical direction is bilaterally asymmetric about theprincipal line of vision, in which the distortion is greater on the noseside and smaller on the ear side.

PRIOR ART DOCUMENTS Patent Documents

-   [Patent Document 1] Japanese published examined application No.    49-3595-   [Patent Document 2] Japanese Unexamined Patent Application    Publication No. 57-10113-   [Patent Document 3] Japanese published examined application No.    H1-5682-   [Patent Document 4] Japanese Unexamined Patent Application    Publication No. H3-230114-   [Patent Document 5] Japanese Unexamined Patent Application    Publication No. H2-216428

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Generally, when the wearer of the spectacle lens moves the line-of-sightto view the front near distance from viewing the front far distance, theline-of-sight of both eyes gradually moves inward to the target to beviewed at near distance. This function of the eye is widely known as theconvergence function. To match the convergence function, generally thenear region of the progressive addition lens is displaced from thedistant region, which is adapted to view the front far distance, towardthe nose side in the horizontal direction. Such a displacement is calledan “amount of inward movement of line-of-sight”.

In the aforesaid Patent Documents 1 to 4, a principal line of vision ofthe progressive addition lens extending vertically from the frontdistance vision toward the front near vision is determined, theprincipal line of vision is treated as a design principal meridian, andthe power progressively changes from the distance power to the nearpower along the principal meridian. Since the position of the front nearvision is displaced toward the nose side in the horizontal direction dueto the aforesaid convergence function of the eye, the principal meridianis a curve that curves toward the nose side from the distant region tothe near region. In other words, in the aforesaid Patent Documents 1 to4, the principal line of vision through which the line-of-sight passesand the design principal meridian are regarded as the same.

However, when the wearer of the progressive addition lens moves theline-of-sight to view the front near distance from viewing the front fardistance, the optical state along the principal line of vision throughwhich the line-of-sight passes is not necessarily in the good opticalstate intended when designing. Particularly, there is a case where thedisplacement of the position at which the optical state of the frontnear vision becomes best (i.e., the amount of design inward movement setbased on the pupillary distance of the wearer and the objectivedistance) is smaller than the amount of inward movement ofline-of-sight, and therefore the binocular vision function is impaired.

Further, there is a case where, when evaluating the progressive additionlens with the lens meter after the lens is designed and trial-produced,the measured amount of inward movement fails reaching the amount ofinward movement of line-of-sight, and therefore the lens is measured ina state where the amount of inward movement is insufficient. Whiledealing with this problem, the inventor of the present inventionrealized that the optical characteristic value measured by, for example,the lens meter (as a measuring device) and the optical characteristicvalue obtained by performing secondary calculation using the measuredvalue are affected by the value of the area of the opening diameter(typically about 6φ to 10φ) of the lens meter.

Examples of the method of calculating the optical characteristic valuewith the lens meter include, for example, the method disclosed in PatentDocument 5 in which the opening diameter is 6φ, for example, and four ormore measurement points, each spaced apart from each other by apredetermined interval, are set within the area of 6φ, and therefractive power calculated based on the refractive state of thesemeasurement points is regarded as the average refractive power withinthe opening diameter. In such case, unless the power distribution iscompletely uniform, a deviation will be actually generated on themeasured refractive power depending on the value of the openingdiameter, i.e., depending on the width of the mutual distance betweenthe four or more measurement points.

Thus, when measuring the average power and the astigmatism, in the casewhere the opening diameter of the lens meter is relatively large andtherefore the deviation is relatively large, the influence of suchdeviation will become nonnegligible. On the other hand, in the casewhere the opening diameter of the lens meter is small, the influence ofsuch deviation will become small. Thus, when evaluating or using themeasured value, it is necessary to consider the influence of the openingdiameter of the lens meter on the measured value. In other words, whenproducing the progressive addition lens, it is necessary to consider theinfluence of the lens meter in both the design step and the productionstep.

In view of the aforesaid problems, it is an object of the presentinvention to improve the optical state of the progressive addition lensalong the principal line of vision through which the line-of-sight ofthe wearer passes by making the displacement of a position at which theoptical state of particularly the front near vision becomes the best tobe the same as the amount of inward movement of line-of-sight, when thewearer moves his (or her) line-of-sight from the front far distance tothe front near distance.

Further, it is another object of the present invention to suitablyevaluate the progressive addition lens by considering the influence ofthe measuring device such as the lens meter or the like.

Means for Solving the Problems

To solve the aforesaid problems, a method of designing a progressiveaddition lens according to an aspect of the present invention is amethod in which an expressionOI<DHis satisfied when: an intersecting line of a line-of-sight of a wearerof the progressive addition lens from a distance vision to a near visionand a refractive surface of the progressive addition lens is defined asa principal line of vision L; in the principal line of vision, aposition corresponding to a front distance vision of the wearer of theprogressive addition lens and a position corresponding to a front nearvision of the wearer of the progressive addition lens are respectivelydefined as a point F and a point ON; a displacement of the point ON fromthe point F toward the nose side in the horizontal direction is definedas an amount of inward movement of line-of-sight OI; an intersection ofa profile curve in horizontal direction H and a principal meridian curveM on the refractive surface of the progressive addition lens is definedas a point DN, in which the profile curve in horizontal direction Hpasses through the point ON in the principal line of vision, and theprincipal meridian curve M passes through the point F of the frontdistance vision and has an interval where power progressively changesfrom an upper portion toward a lower portion of the progressive additionlens; a displacement of the point DN of the design principal meridiancurve M from the point F of the front distance vision toward the noseside in the horizontal direction is defined as an amount of designinward movement DH.

Further, a progressive addition lens according to another aspect of thepresent invention is a lens in which an amount of design inward movementDH is greater than an amount of inward movement of line-of-sight OI,when: in a refractive surface of the progressive addition lens, aprincipal meridian curve M passing through a point F of a front distancevision and having an interval where power progressively changes from anupper portion toward a lower portion of the progressive addition lens isset, and a displacement of a point DN of the design principal meridiancurve M from the point F of the front distance vision toward the noseside in the horizontal direction is defined as the amount of designinward movement DH, an intersecting line of a line-of-sight of theprogressive addition lens from a distance vision to a near vision andthe refractive surface of the progressive addition lens is defined as aprincipal line of vision L, and a displacement of a point ON of a frontnear vision of the principal line of vision from the point F of thefront distance vision toward the nose side in the horizontal directionis defined as the amount of inward movement of line-of-sight OI.

In the progressive addition lens and the design method thereof accordingto the present invention, the relation of the “amount of design inwardmovement DH” and the “amount of inward movement of line-of-sight OI”,which were confused with each other in the conventional progressiveaddition lens, is individually considered, particularly the relation ofthe both is OI<DH. Thus, by more greatly displacing the amount of designinward movement DH, as a value greater than the amount of inwardmovement of line-of-sight OI instead of being treated as the amount ofinward movement of line-of-sight OI, from the point F toward the noseside in the horizontal, it is possible to bring a position at which therefractive power reaches the maximum peak or a position at which theastigmatism distribution reaches the minimum peak (for example, zero) inthe profile curve in horizontal direction H, which passes through thepoint ON, close a position where the amount of inward movement ofline-of-sight becomes OI, in the case where the average power orastigmatism is smoothed within a range of a pupil diameter for example.

Further, it is preferred that the method of designing the progressiveaddition lens according to the aforesaid aspect of the present inventionincludes the steps of: setting the amount of inward movement ofline-of-sight OI and the pupil diameter E; performing smoothingprocessing on the average power distribution and the astigmatismdistribution within the area of the pupil diameter E; calculating theamount of inward movement VH of the peak position VN of the smoothedaverage power or the smoothed astigmatism and obtaining an error ofinward movement based on the difference (VH-OI) between the amount ofinward movement VH and the amount of design inward movement DH; andrepeatedly performing calculation by changing the value of the amount ofdesign inward movement DH until the absolute value of the amount oferror of inward movement (VH-OI) is within a predetermined threshold, sothat the amount of inward movement VH becomes close to the amount ofinward movement of line-of-sight OI.

By including the aforesaid steps, the amount of inward movement VH ofthe peak position VN corresponding to the peak value in the smoothedaverage power distribution or the peak value in the smoothed astigmatismdistribution (the peak value is the minimum value in the case of theastigmatism distribution) can be reliably brought close to the amount ofinward movement of line-of-sight OI by relatively simple calculationmethod, so that the difference between the amount of inward movement VHand the amount of inward movement of line-of-sight OI does not exceedthe predetermined threshold.

Further, a method according to further another aspect of the presentinvention is a method for evaluating a progressive addition lens whichis designed so that at least one of an average power distribution and anastigmatism distribution is bilaterally asymmetrical in the horizontaldirection with a design principal meridian curve as a boundary, themethod comprising: taking into consideration of an error caused bysmoothing the average power distribution or the astigmatism distributionwithin a measurement range of a lens meter between an amount of inwardmovement, as a target value, at a position corresponding to a front nearvision and an inspected value of the lens meter, correcting an error ofan inspection position where the amount of inward movement is inspectedby the lens meter, and evaluating the amount of inward movement at thecorrected inspection position.

Further, a method according to further another aspect of the presentinvention is a method for evaluating a progressive addition lens whichis designed so that at least one of an average power distribution and anastigmatism distribution is bilaterally asymmetrical in the horizontaldirection with a design principal meridian curve as a boundary, themethod comprising: taking into consideration of an error caused bysmoothing the average power distribution or the astigmatism distributionwithin a measurement range of a lens meter between an amount of inwardmovement, as a target value, at a position corresponding to a front nearvision and an inspected value of the amount of inward movement obtainedby the lens meter, correcting an error of the inspected value of theamount of inward movement obtained by the lens meter, and evaluating theamount of inward movement based on the corrected inspected value.

Thus, by previously correcting the error of the inspection positionwhere the amount of inward movement is inspected by the lens meter andevaluating the amount of inward movement at the corrected inspectionposition, it is possible to avoid detecting unnecessary error of theamount of inward movement caused by the opening diameter of the lensmeter and therefore more suitably perform evaluation of the amount ofinward movement.

Incidentally, the lens meter mentioned in the specification and claims 9to 12 of the present invention collectively means very kinds ofmeasuring devices used for measuring refractive value of the lens.

Advantages of the Invention

With the progressive addition lens and the design method thereofaccording to the present invention, by individually considering thedesign principal meridian curve and the principal line of vision whenthe wearer actually moves the line-of-sight, it is possible to designthe progressive addition lens so as to obtain an amount of inwardmovement of line-of-sight as intended as designed. To be specific, bysetting an amount of design inward movement which is greater than theamount of inward movement of line-of-sight intended when designing, itis possible to obtain an amount of inward movement of line-of-sight asintended as designed, and therefore it is possible to provide spectacleswhich are less likely to impede binocular vision.

Further, with the progressive addition lens and the design methodthereof according to the present invention, it is possible to considerthe influence of the lens meter and suitably evaluate the progressiveaddition lens.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view of a progressive addition lens for right eye;

FIG. 2 is a cross section of the progressive addition lens shown in FIG.1 when viewed from the lateral side;

FIG. 3A is a graph showing a refractive power distribution along aprofile curve in horizontal direction indicated by dotted line H shownin FIG. 1.

FIG. 3B is a graph showing a smoothed refractive power distributionobtained by averaging the refractive power distribution shown in FIG. 3Awith the width of pupil diameter;

FIG. 3C is a graph obtained by superimposing the graph of FIG. 3A andthe graph of FIG. 3B on each other;

FIG. 4 is a front view of a progressive addition lens for right eyeaccording to an embodiment of a progressive addition lens of the presentinvention;

FIG. 5 is a view showing an example of an average power distribution ofa progressive addition lens according to a prior art;

FIG. 6 is a view showing an example of an astigmatism distribution ofthe progressive addition lens according to the prior art;

FIG. 7 is a view showing an example of an average power distribution ofthe progressive addition lens according to the embodiment of the presentinvention;

FIG. 8 is a view showing an example of an astigmatism distribution ofthe progressive addition lens according to the embodiment of the presentinvention;

FIG. 9 is a flowchart for explaining a method of designing theprogressive addition lens according to the present invention;

FIG. 10A is a front view of a progressive addition lens for right eyemade for explaining a method for evaluating the progressive additionlens according to the present invention;

FIG. 10B is a graph showing a refractive power distribution of averagepower of the progressive addition lens for right eye shown in FIG. 10A;

FIG. 11A is a front view of a progressive addition lens for right eyemade for explaining the method for evaluating the progressive additionlens according to the present invention;

FIG. 11B is a graph showing a refractive power distribution of averagepower of the progressive addition lens for right eye shown in FIG. 11A;

FIG. 12A is a front view of a progressive addition lens for right eyemade for explaining the method for evaluating the progressive additionlens according to the present invention;

FIG. 12B is a graph showing a refractive power distribution of averagepower of the progressive addition lens for right eye shown in FIG. 12A;and

FIG. 13 is a flowchart for explaining the method for evaluating theprogressive addition lens according to the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below, however itshould be understood that the present invention is not limited to theseembodiments. The description will be made in the following order:

[1] Embodiment of Progressive Addition Lens and Embodiment of DesignMethod of Progressive Addition Lens

(1) Description of Principle of Design Method of Progressive AdditionLens

(2) Description of Progressive Addition Lens having HorizontallyAsymmetric Design

(3) Embodiment of Progressive Addition Lens

(4) Flowchart of Design Method of Progressive Addition Lens

[2] Embodiment of Evaluation Method for Progressive Addition Lens

[1] Embodiment of Progressive Addition Lens and Embodiment of DesignMethod for Progressive Addition Lens

(1) Description of Principle of Design Method of Progressive AdditionLens

Before describing the embodiments of the present invention, as a premisethereof, the terms and positional relation necessary for describing theprogressive addition lens will be clearly defined with reference to theattached drawings.

FIG. 1 is a front view showing a progressive addition lens Q1 for righteye when viewed from a convex side, and is made for explaining theprinciple of the present invention. In FIG. 1, the intersecting line ofa line-of-sight of a wearer of the progressive addition lens Q rangingfrom a distance vision to a near vision and a refractive surface of theprogressive addition lens Q1 is called “principal line of vision” L.Incidentally, the “line-of-sight” here is defined as a line with nowidth, and the principal line of vision L is a movement locus of anintersection of the line of vision of the wearer and the lens surfaceplotted by moving the eye up and down when the pupil is considered as apoint. In other words, the principal line of vision L is defined as acurve without considering the pupil diameter. Further, the position offront distance vision in the principal line of vision is a point F, andthe position of front near vision in the principal line of vision is apoint ON.

Here, the point ON is displaced from the point F toward the nose side inthe horizontal direction, and such displacement OI is called “amount ofinward movement of line-of-sight”. The amount of inward movement ofline-of-sight OI is optically designed based on the pupillary distanceof the wearer of the progressive addition lens and an objective distance(an near vision objective distance defined by a client, i.e., the wearerof the spectacles, a spectacles store, a lens manufacturer or the like)so that the best visual acuity of the near vision (or the best visualacuity of a particular usage) can be obtained.

Further, there is a “design principal meridian curve” M on therefractive surface of the progressive addition lens Q1, wherein thecurve M passes through the point F and has an interval along which thepower progressively changes from an upper portion toward a lower portionof the lens. In the curve M, a point having a height corresponding tothe near vision (i.e., an intersection of a profile curve H inhorizontal direction, which passes through the point ON, and the curveM) is called a “point DN”. At this time, a point DH is displaced fromthe point F toward the nose side in the horizontal direction, and suchdisplacement is called “amount of design inward movement”.

In other words, it can be said that the “principal line of vision” L isa curve through which the line-of-sight passes while the vision of thewearer of the spectacles is changed from the front distance vision tothe front near vision, and the “design principal meridian curve” M is adesign reference curve for providing change of the progressive-power.

In the aforesaid prior arts, the aforesaid two curves L and M aretreated as the same without distinction. In other words, the “principalline of vision” L is simply regarded as the “design principal meridiancurve” M for providing change of the progressive-power, or change of theprogressive-power is provided along the “design principal meridiancurve” M, and righteously the curve M is treated as the “principal lineof vision” L.

Incidentally, since the refractive surface of the progressive additionlens includes a refractive surface on object side and a refractivesurface on eye side, the refractive surface having the “principal lineof vision” L and “design principal meridian curve” M also includes twotypes of refractive surfaces, which are a front type refractive surfaceand a rear type refractive surface.

Further, change of the progressive-power along the “principal line ofvision” L and the “design principal meridian curve” M includes twocases, which are a case where the change of the progressive-power is thechange of the surface refractive power (in the case of a single-surfaceprogressive addition lens), and a case where the change of theprogressive-power is the change of the refractive power transmittedthrough the lens (in the case of a both-surface progressive-additionlens).

Although the after-mentioned embodiments are described mainly based on acase where the surface refractive power on the object side changes, itshould be understood that the present invention may also be applied to acase where the surface refractive power on the eye side changes and acase where the transmitted refractive power changes, and the progressiveaddition lens, the after-mentioned design method of the progressiveaddition lens and the evaluation method according to the presentinvention include all these cases.

Furthermore, although the positions of the “principal line of vision” Land the “design principal meridian curve” M in a range from the frontdistance vision to the upward portion and a range from the front nearvision to the downward portion have not been defined in the abovedescription, it is considered that all these curves substantially extendup and down as shown in FIG. 1 for the sake of convenience.

FIG. 2 is a cross section of the progressive addition lens Q1 shown inFIG. 1 when viewed from the lateral side. FIG. 2 shows that the verticalposition of the point F and point ON changes depending on whether therefractive surface, on which the “principal line of vision” L and the“design principal meridian curve” M exist, is on the object side or onthe eye side. The last number “1” of the reference numerals of FIG. 2represents the case where the refractive surface, on which the point Fand point ON are set, is on the object side, and the last number “2”represents the case where the refractive surface is on the eye side.

In each of the aforesaid Patent Documents 1 to 4, the progressiveaddition lens is divided into two portions which are a nose side portionand an ear side portion, and the “principal line of vision”, as aboundary of the two portions, is regarded as the same as the “designprincipal meridian curve”. In these Patent Documents, in which the“design principal meridian curve” is regarded as a theoretical referencecurve without width, there are not only examples where the opticalproperty on the nose side and the optical property on the ear side arehorizontally symmetrical with each other such as disclosed in PatentDocuments 1 and 2, but also examples where the optical property on thenose side and the optical property on the ear side are horizontallyasymmetrical with each other such as disclosed in Patent Documents 3 and4.

In contrast, the inventor of the present invention thinks the “principalline of vision” is the intersecting line of the line-of-sight of thespectacles wearer and the lens surface, and treats the “principal lineof vision” as different from the “design principal meridian curve”. Inother words, the “line-of-sight” is generally treated as a strait linewithout width, however the light incident into the eye along theline-of-sight is actually a light beam passed through the pupil diameterwhich has a diameter of about 2 mm to 8 mm. Thus, the “line-of-sight”may also be considered as a path of the light incident into the eyepassed through the center of the pupil diameter.

Based on this point of view, in a progressive addition lens where therefractive power is horizontally asymmetrical with the “design principalmeridian curve” as a boundary, since in the whole light beam passedthrough the pupil diameter, the half portion light beam on the nose sideand the half portion light beam on the ear side have different theoptical property, the averaged optical property of the whole light beamis different from the optical property of the light passed through thecenter of the pupil. Here, the disadvantages of the prior arts will bedescribed below with reference to FIGS. 3A, 3B and 3C.

FIGS. 3A, 3B and 3C are each a graph showing a refractive powerdistribution of average power along a profile curve H in horizontaldirection indicated by a dotted line of FIG. 1. The profile curve Hpasses through the point ON in the “principal line of vision” and thepoint DN in the “design principal meridian curve” in the front nearvision.

The solid line of FIG. 3A indicates the refractive power distributionitself along the profile curve H. As is known from FIG. 3A, therefractive power distribution along the profile curve H is anasymmetrical distribution in which the refractive power reaches Pdh,which is the peak, at the point DN in the “design principal meridiancurve” and decreases more rapidly on the nose side than on the ear sidewith Pdh as a boundary.

FIG. 3B is a dotted line graph obtained by replacing the solid linegraph of FIG. 3A by a smoothed refractive power distribution obtained byaveraging the solid line graph with the width of the pupil diameter. Thehorizontal width of the hatched areas of FIG. 3A represents the pupildiameter, and the dotted line graph of FIG. 3B is obtained bytranscribing the graph by using the average value of the hatched area asthe value of the central position of the pupil diameter.

For example, since the refractive power in the left hatched area of FIG.3A changes uniformly within the range of the pupil diameter, the valueof the central position of the pupil diameter is equal to the averagevalue of the hatched area (indicated by the leftmost open circle of FIG.3B). Thus, it can be confirmed by viewing FIG. 3C, which is a graphobtained by superimposing the graph of FIG. 3A and the graph of FIG. 3Bon each other, that the values of both graphs at this position have nodifference.

However, the refractive power in the right hatched area of FIG. 3A doesnot change uniformly within the range of the pupil diameter. To bespecific, with Pdh as the peak, since the refractive power on the bothsides of Pdh is lower than Pdh, the average value of the hatched area(indicated by the rightmost open circle of FIG. 3B) is lower than thevalue of the central position of the pupil diameter. This can also beconfirmed by viewing the graph of FIG. 3C.

Similarly, it can be confirmed that the value of Pvn, which is the peakof the dotted line graph of FIG. 3B, is lower than the value of Pdn,which is the peak of the solid line graph of FIG. 3A. This is a resultof smoothing process which is achieved by averaging the graph with thewidth of the pupil diameter as mentioned above. Incidentally, inaddition to the moving-average method with the width of the pupildiameter described above, the smoothing methods also include othermethods such as a polynomial fitting method, a frequency-domain methodand the like. All these methods share a common feature that, in order tosmooth concavity and convexity of the graph, in the aforesaid comparisonbetween the peak values, there is a tendency that Pdn>Pvn.

It should be noted that, in the case where the refractive powerdistribution along the profile curve H is asymmetrical between the earside and the nose side with the refractive power Pdn at the point DN ofthe “design principal meridian curve” as a boundary, the displacement VHof Pvn is different from the displacement DH of Pdn.

In other words, as mentioned above, the solid line graph of FIG. 3A isan example in which the refractive power distribution along the profilecurve H is an asymmetrical distribution in which the refractive powerdecreases more rapidly on the nose side than on the ear side with Pdh asa boundary. It can be known that, in the aforesaid asymmetricaldistribution example, if moving the hatched area of FIG. 3A along thehorizontal direction to complete the dotted line graph of FIG. 3B, forexample, the position of Pvn will be closer to the center than theposition of Pdn, and therefore VH<DH.

It is easy to presume that, in an example where the asymmetricaldistribution corresponds to a graph inverted from the graph of FIG. 3A(i.e., in an example where the refractive power distribution along theprofile curve H is an asymmetrical distribution in which the refractivepower decreases more rapidly on the ear side than on the nose side withPdh as a boundary), the position of Pvn will be closer to the nose sidethan the position of Pdn, and therefore VH>DH.

Further, the position of Pvn and the position of Pdn are the same andtherefore VH=DH in the case where the refractive power distributionalong the profile curve H is symmetrical with Pdn as a boundary.

Thus, in the aforesaid prior arts (Patent Documents 1 to 4),particularly in the horizontally asymmetrical prior arts with the“design principal meridian curve” as a boundary, it is impossible toobtain a correct predetermined “amount of inward movement ofline-of-sight” as long as the “principal line of vision” and the “designprincipal meridian curve” are treated as the same.

For example, in the progressive addition lens Q1 for right eye as shownin FIG. 1, the details of the power detail are: spherical power S=+4.50,addition power Add=2.50, distance fitting point is F, and near additionpower measurement point is DN. Herein, the point DN is displaced fromthe point F toward the nose side in the horizontal direction by DH thatis equal to the predetermined “amount of inward movement ofline-of-sight” OI, and in this example, OI=DH=4.0 mm.

However, in the example of FIG. 1, the refractive power distributionalong the profile curve H in horizontal direction changes more rapidlyin the range from the point DN to the nose side than in the range fromthe point DN to on the ear side, and therefore if the pupil diameter ofthe wearer of the lens is 6.0 mm, for example, the amount of inwardmovement VH of the peak Pvn of the average refractive power, which isobtained by averaging the refractive power with the width of the pupildiameter, will be 0.3 mm smaller than DH, i.e., VH=3.7 mm. Thus, it isimpossible to obtain the correct predetermined “amount of inwardmovement of line-of-sight” OI.

Incidentally, although FIGS. 3A, 3B and 3C are made to explain therefractive power distribution, the astigmatism distribution can also beexplained using these drawings. In the case where the drawings are usedto explain the astigmatism distribution, the vertical axis will be theabsolute value of the astigmatism, instead of being the refractivepower. In such a case, the higher the vertical axis goes, the smallerthe absolute value of the astigmatism becomes; and the lower thevertical axis goes, the greater the absolute value of the astigmatismbecomes. In other words, the peak of each drawing represents a positionwhere the absolute value of the astigmatism is the smallest.

A principal meridian where the minimum value of the absolute value ofthe astigmatism on the refractive power is zero is called an “umbilicalprincipal meridian”, however in the present invention, the existence ofthe “umbilical principal meridian” is not necessary, and a principalmeridian where the astigmatism incident into the eye transmitted throughthe lens becomes the minimum value may be regarded as the “designprincipal meridian curve”. In such a case, each graph in FIGS. 3A, 3Band 3C is treated as “transmission astigmatism”, instead of surfaceastigmatism on the refractive surface.

(2) Description of Progressive Addition Lens Having HorizontallyAsymmetric Design

As described above, the advantages of the present invention can beachieved in the case where the lens is horizontally asymmetrical withthe “design principal meridian curve” as a boundary. The horizontallyasymmetric design, to which the present invention is applied, will bebriefed below, and the reasons why the horizontally asymmetric design isbeneficial for achieving good binocular vision will also be describedbelow.

First, to achieve good binocular vision, it is necessary to make aposition of the right lens through which the line-of-sight of the righteye passes have the same optical performance as a position of the leftlens through which the line-of-sight of the left eye passes, wherein theoptical performance includes astigmatism, axial direction ofastigmatism, average refractive power (spherical power+half ofcylindrical power), and horizontal component and vertical component ofprism refractive power of the lens.

Here, in the case where the target to be viewed is moved from the frontside toward the lateral side of the lens wearer, since the line-of-sightof one eye moves toward the ear side and the line-of-sight of the othereye moves toward the nose side, a position of the one lens through whichthe line-of-sight of the one eye passes will not necessarily have thesame optical performance as a position of the other lens through whichthe line-of-sight of the other eye passes. If the target to be viewed isat an infinite distance from the lens wearer, since the deflection angleof the line-of-sight of the right eye and the deflection angle of theline-of-sight of the left eye are the same when the target to be viewedis moved from the front vision toward the side vision, it is preferredthat the distribution of the optical performance of the lens isbilaterally mirror symmetric in the horizontal direction with theprincipal line of vision as a boundary (i.e., a symmetrical arrangementin which an image is reflected in a mirror disposed at the position ofthe principal line of vision).

On the other hand, if the target to be viewed is at a finite distancefrom the lens wearer, due to convergence, both the line-of-sight of theright eye and the line-of-sight of the left eye will be moved toward thenose side. In such state, when the target to be viewed is moved from thefront vision toward the side vision, distance to the target to be viewedwill become farther in great generality. If the distance to the targetto be viewed becomes farther, the convergence of the eye will becomesmaller, and therefore the line-of-sights of both eyes will become moreclosely parallel with each other. Thus, if the target to be viewed is ata finite distance from the lens wearer, the deflection angle of theline-of-sights of the right eye and the deflection angle of theline-of-sights of the left eye will be different from each other whenthe target to be viewed is moved from the front vision toward the sidevision, and the line-of-sight rotated toward the ear side will be moregreatly deflected than the line-of-sight rotated toward the nose side.Due to the rotation of the head of the lens wearer in side vision(typically about half of the angle of movement from the front visiontoward the side vision is achieved by rotating head, and the other halfis achieved by rotating eye), such trend is further condensed in thespectacle lens that rotates concomitantly with the head, and thereforebecomes prominent. Thus, to view the finite distance, it is preferredthat the portion where the principal line of vision is displaced towardthe nose side with the position of the point F as a reference isbilaterally asymmetrical in the horizontal direction. In a progressiveaddition lens, since the distribution of the optical performance of thelens from the principal line of vision toward the horizontal directiongenerally changes, it is preferred that optical performance changes morerapidly in the range from the principal line of vision toward the noseside than in the range from the principal line of vision toward the earside so that the position of the right lens through which theline-of-sight of the right eye passes has the same optical performanceas the position of the left lens through which the line-of-sight of theleft eye passes.

It can be said by summarizing above description that, in one or all ofthe following five changes along the profile curve H in horizontaldirection that intersects with the point ON of the “principal line ofvision”, it is preferred that the change is more rapid in the range fromthe point ON toward nose side than in the range from the point ON towardear side.

1. Change of the astigmatism distribution

2. Change of the axial direction of astigmatism

3. Change of the average refractive power

4. Change of the horizontal component of prism refractive power

5. Change of the vertical component of prism refractive power

The concrete implementation method to which the present invention isapplied has no big difference from the conventional methods with respectto the horizontally asymmetric design, which is the subject of thepresent invention. The important thing is that the position of the“principal line of vision”, by which the predetermined progressiveeffect is obtained, and the position of the “design principal meridiancurve”, which provides progressive effect on optical design, aredifferent from each other. In other words, the result of themoving-average with the pupil diameter having a diameter of 2 mm to 8 mmcan be obtained by estimating the “amount of design inward movement” DH,which is different from the “amount of inward movement of line-of-sight”OI, so that the “amount of design inward movement” DH becomes thepredetermined “amount of inward movement of line-of-sight” OI.

Although it is possible to set up a relational expression between theamount of design inward movement DH and the amount of inward movement ofline-of-sight OI, the simplest method is performing convergencecalculation by means of iterative calculation. For example, assumingthat the maximum difference between the amount of design inward movementDH and the amount of inward movement of line-of-sight OI is 5 mm and thefinal allowable error is ±0.05 mm, then the convergence ratio is 1/100,and convergence can be achieved by performing only seven times iterativecalculations even by means of half-convergence calculation, which thesimplest calculation.

(3) Embodiment of Progressive Addition Lens

An embodiment of the present invention will be described below withreference to FIG. 4. FIG. 4 is a front view of an example of theprogressive addition lens Q according to the embodiment of the presentinvention. The details of the power of the progressive addition lens Qof the present example are, for example, spherical power S=+4.50,addition power Add=2.50; the distance fitting point is F; and theposition located in the principal line of vision L, which passes throughthe point F, and corresponding to the front near vision is the point ON.Herein, the point ON is displaced from the distance fitting point Ftoward the nose side in the horizontal direction by the predetermined“amount of inward movement of line-of-sight” OI, and in the presentexample OI=4.0 mm.

Further, on the object side refractive surface of the progressiveaddition lens Q of the present example, there is a “design principalmeridian curve” M which passes through the distance fitting point andalong which the power progressively changes from the upper portion tothe lower portion. Further, the point DN is at the “intersection of thedesign principal meridian curve” M and the profile curve in horizontaldirection H that passes through the point ON. Incidentally, the point DNis displaced from the distance fitting point F toward the nose side inthe horizontal direction by DH, and DH is greater than OI by design. Inthe present example, DH=4.3 mm.

In other words, in such a case, the refractive power distribution alongthe profile curve H in horizontal direction changes more rapidly in therange from the point DN to the nose side than in the range from thepoint DN to on the ear side, and the diameter of the pupil diameter ofthe wearer is 6.0 mm when the lens is actually worn by the wearer. Thus,in order to make the amount of inward movement VH of the point VN (whichis the peak position of the smoothed distribution within the pupildiameter) become the predetermined amount of inward movement (i.e., the“amount of inward movement of line-of-sight” OI=4.0 mm, in the bestoptical state), the relation between the “amount of design inwardmovement” DH and the “amount of inward movement of line-of-sight” OI isestimated by performing convergence calculation by means of iterativecalculation. Further, based on the estimated result, it is calculatedthat the “amount of design inward movement” DH should be DH=4.3 mm inthis case, which is 0.3 mm greater than the predetermined “amount ofinward movement of line-of-sight” OI=4.0 mm.

FIG. 5 is a view showing an average power distribution of a progressiveaddition lens for right eye according to a prior art, and FIG. 6 is aview showing an astigmatism distribution of the progressive additionlens for right eye according to the prior art, the drawings beingplotted as a comparison with the embodiment of the present invention. Inthis example, similar to the example described with reference to FIG. 1,the details of the power are: spherical power S=+4.50, addition powerAdd=2.50, and OI=DH=4.0 mm.

As is known from FIGS. 5 and 6 that, an intersection DNa of a profilecurve Ha in horizontal direction (corresponding to the profile curve Hof FIG. 1) and a “design principal meridian curve” Ma is displaced froma front distance vision Fa toward the nose side in the horizontaldirection by a predetermined “amount of design inward movement” DHa, andan amount of inward movement of a point VNa (which is the peak of theaverage refractive power distribution obtained by smoothing therefractive power distribution with the width of the pupil diameter inthe case where the diameter of the pupil diameter is 6.0 mm) is VHa=3.7mm, which is smaller than DHa, so that amount of the inward movement isinsufficient.

Incidentally, the small circle plotted by the dotted line in the nearportion indicates the pupil diameter in the both drawings. Since thecontour distribution of the average power and the contour distributionof the astigmatism are not displaced in the horizontal direction, it ispossible to presumed that, at the position VNa indicated by the opencircle at the center of the small circle, the average refractive poweralong the profile curve Ha in horizontal direction reaches the maximumvalue and the astigmatism reaches the minimum value. In other words, theposition VNa in the near vision is the actual center when viewing neardistance through the pupil diameter, and the amount of inward movementVHa of VNa is smaller than the predetermined position DHa, which isindicated by the filled circle, so that it is obvious that the amount ofthe inward movement is insufficient.

FIG. 7 is a view showing an average power distribution of theprogressive addition lens for right eye of the aforesaid embodiment ofthe present invention, and FIG. 8 is a view showing an astigmatismdistribution of the progressive addition lens for right eye of theaforesaid embodiment of the present invention. In this example, similarto the example described with reference to FIG. 4, the details of thepower are: spherical power S=+4.50, addition power Add=2.50, and OI=4.0mm, but the amount of design inward movement DH is greater than OI.

As shown in FIGS. 7 and 8, in the progressive addition lens Qb, anintersection DNb of a “design principal meridian curve” Mb and a profilecurve Hb in the horizontal direction (corresponding to the profile curveHa of FIGS. 5 and 6) is displaced from a front distance vision Fb towardthe nose side in the horizontal direction by DHb, which is slightlygreater than DHa. In other words, DHb=4.3 mm, and DHb>OI in this case.At this time, when the point which represents the peak of the averagerefractive power distribution obtained by smoothing the refractive powerdistribution with the width of the pupil diameter is a point VNbindicated by the filled circle in the case where the diameter of thepupil diameter is 6.0 mm, the point VNb is correctly displaced from thedistance vision position Fb toward the nose side in the horizontaldirection by a predetermined “amount of inward movement ofline-of-sight” VHb (=OI=DHa), and conversely the “amount of designinward movement” DHb, which is the position of DNb indicated by the opencircle, is greater than VHb. Thus, in the present embodiment shown inFIGS. 7 and 8, the amount of inward movement of line-of-sight VHb iscorrectly obtained.

(4) Flowchart of Design Method of Progressive Addition Lens

FIG. 9 is a flowchart for explaining a design method of the asymmetricalprogressive addition lens according to the present invention. As shownin FIG. 9, when staring the design of the progressive addition lens ofthe present invention, a targeted amount of inward movement ofline-of-sight OI and pupil diameter E are set first (Step S1). Next, theamount of inward movement of line-of-sight OI is substituted as initialvalue of the amount of design inward movement DH (Step S2). Thereafter,the average power distribution and the astigmatism distribution of thelens designed by the aforesaid setting are obtained (Step S3).Thereafter, by performing smoothing processing on the obtained averagepower distribution and astigmatism distribution in the area of the pupildiameter E, a new average power distribution and a new astigmatismdistribution are obtained (Step S4).

Next, the amount of inward movement VH of the peak position VN of thesmoothed average power or the smoothed astigmatism, which are smoothedalong the profile curve H in horizontal direction passing through thepoint ON corresponding to the front near vision, is obtained (Step S5),and further the difference (VH−OI), which represents the error of inwardmovement, is obtained (Step S6). Thereafter, it is judged whether or notthe absolute value of the error, i.e., the absolute value of (VH−OI), iswithin a threshold of 0.05 mm (Step S7). If the absolute value of theerror is less than the threshold, then it is judged that the amount ofinward movement of line-of-sight VH substantially converges at thepredetermined amount of inward movement OI, and therefore the processingis completed. If the absolute value of the error is equal to or greaterthan the threshold, then half (½) of the “error of inward movement”(VH−OI) obtained in Step S6 is subtracted from the “amount of designinward movement” DH obtained in Step S2 to obtain a new “amount ofdesign inward movement” DH. In other words, the processing is returnedto Step S3 to perform convergence calculation, by means of iterativecalculation with a new amount of design inward movement ofDH=DH−(VH−OI)/2 (Step S8).

Incidentally, the reason why the amount subtracted from the amount ofdesign inward movement DH in Step S8 is half of the “error of inwardmovement” instead of being the whole “error of inward movement” isbecause it is desirable to avoid the possibility that the error might beincreased when performing the recalculation and therefore thecalculation might diverge instead of converging. Further, since theseventh power of ½ is equal to 1/128, it is anticipated that at leastthe error can be made equal to or less than 1/128 by repeating at most 7times iterative calculations, and therefore the absolute value of theerror can be made smaller than the threshold in a relatively short time.

As described below, by using the aforesaid design method of theprogressive addition lens, impairment of binocular vision function canbe suppressed.

The binocular vision function originally means highly sophisticatedfunction such as simultaneous vision, stereoscopic vision and fusionowned by a visual system including the brain, instead of being afunction owned by spectacles or spectacle lens. However, all thesefunctions such as simultaneous vision, stereoscopic vision and fusionare based on the premise of good binocular vision, and it is obviousthat the use of spectacles to impede binocular vision will result inimpairment of the binocular vision function.

In other words, the advantage of the present invention is that therelation of the “amount of design inward movement” and the “amount ofinward movement of line-of-sight”, which were confused with each otheraccording to the prior arts, is made clear, and as a result, the methodof obtaining a correct predetermined “amount of inward movement ofline-of-sight” becomes clear, so that it becomes possible to providespectacles which are less likely to impede binocular vision.

[2] Embodiment of Evaluation Method for Progressive Addition Lens

Next, an embodiment of evaluation method for progressive addition lensaccording to the present invention will be described below. Theevaluation of the optical characteristics (such as power, refractivepower distribution state, layout position and the like) of theprogressive addition lens is performed after the lens is designed andthen trial-produced according to the design. To be specific, as the flowof a typical production process of the progressive addition lens, thelens is designed first. In the designing step, when determining thearrangement of the design principal meridian curve, the amount of inwardmovement is determined and laid out on the lens.

Further, while the processing is transferred from the designing step tothe production step, there is a trial production step in which it isnecessary to verify whether or not the production of the lens isperformed according to the design. The verification of the lens isperformed using a lens meter, such as the one described in the aforesaidPatent Document 5 and the like, to check whether the value at each ofpreset check points (inspection positions) meets the designrequirements. The amount of inward movement is also checked using thesemethods in which the lens meter is placed on the designated inwardmovement position to verify whether the position has a design opticalvalue (inspected value).

However, as described above, the measured value obtained by the lensmeter is an average value within the opening diameter of the lens meter(although average calculation method is different depending on the lensmeter), the opening diameter of the lens meter will have influenceparticularly on the measurement of the amount of inward movement. To bespecific, similar to the smoothing process in the area within the pupildiameter described with reference to FIGS. 3A, 3B and 3C, there is anaverage refractive power as a result of performing averaging processwithin the area of the opening diameter of the lens meter, and in aprogressive addition lens having horizontally asymmetric design, thepeak position where the average refractive power reaches the peak isdisplaced toward a side where change of the refractive powerdistribution is thinner, typically the ear side (the temple side). Inother words, if the position where the average refractive power withinthe opening diameter of the lens meter reaches the peak is a measurementposition MN, then an amount of inward movement MH of the measurementposition MN will be smaller than the amount of inward movement DH of thepoint DN that is the intersection of design principal meridian curve Mand the profile curve H.

Conventionally, even in the case where wrong verification result iscaused due to the influence of the measurement error of such measuringdevice although the processing of the lens is actually performedaccording to the design, the evaluation is performed based on themeasured value without considering the influence of the measurementerror of the measuring device. Thus, if the amount of inward movement isrevised (corrected) according to the measured value itself of themeasuring device, there will arise a problem that the amount of inwardmovement might be different from the amount of design inward movement.

In other words, since the position of the design principal meridiancurve obtained based on the measured data is not correctly grasped dueto the influence of the opening diameter of the lens meter (i.e., themeasuring device), as a result the position of the best optical state offront near vision for the wearer is displaced.

In contrast, in the present invention, since the measurement position onthe lens is selected taking into consideration of the influence of theopening diameter of the lens meter, it is possible to avoid wrongcorrection to the amount of inward movement caused by the aforesaiderror of the measuring device.

First, a case where the measurement is performed on a conventionalprogressive addition lens will be described below with reference toFIGS. 10A and 10B. FIG. 10A is made for explaining the measurementposition when evaluating the optical characteristics of a progressiveaddition lens Q1, and is a front view of the progressive addition lensfor right eye. The progressive addition lens Q1 has the sameconfiguration as the progressive addition lens for right eye Q1described with reference to FIG. 1, in which a principal line of visionL and a design principal meridian curve M are the same. As shown in FIG.10B, a refractive power distribution of the average power along theprofile curve H in horizontal direction, which passes through a point ONwhich is a position corresponding to the front near vision of theprincipal line of vision L, is denser on the nose side and thinner onthe ear side with a peak value Pdn at the point ON (=DN) as a boundary.Here, in the case where the opening diameter D of the lens meter is, forexample, 8 mm, the averaged distribution in this range (i.e., in thehatched area in FIG. 10B) is indicated by a dashed line shown in FIG.10B, and a peak value Pmn of the averaged distribution is lower than thedesign peak value Pdn, and further, the point MN, which is a position inthe profile curve H corresponding to the peak value Pmn of the averageddistribution, is at a position displaced from the point ON toward theear side. Thus, the point MN can be selected as the measurement positionof the lens meter having the opening diameter D.

A case of evaluating a progressive addition lens designed using theaforesaid design method of the progressive addition lens according tothe present invention will be described below. FIG. 11A is a front viewof a progressive addition lens for right eye Q, which has the sameconfiguration as the progressive addition lens Q shown in FIG. 4. Theprogressive addition lens Q is designed so that, with respect to theprincipal line of vision L, the design principal meridian curve M isdisplaced toward the nose side where the average power distribution orthe astigmatism distribution is denser, according to the pupil diameterof the wearer of the lens. In FIG. 11A, like components are denoted bylike reference numerals as of those of FIG. 4, and the explanationthereof will be omitted.

Regarding the measurement position of the progressive addition lens Q inthe case where the opening diameter D of the lens meter is greater thanthe pupil diameter E, there is an example of the refractive powerdistribution of the average power shown in FIG. 11B in which the peakvalue Pvn of the averaged distribution within the area of the pupildiameter E becomes smaller than the design peak value Pdn, and the peakvalue Pmn of the averaged distribution within the area of the openingdiameter D of the lens meter becomes further smaller. Further, since thegreater the width of the averaged area is, the more greatly the positionof the peak value is displaced toward the side where the distribution isthinner, the point MN (which is the position of the profile curve Hcorresponding to the peak value Pmn) is displaced from the point ON(=VN)(which is the position corresponding to the peak value Pvn) towardthe ear side. In such a case, as shown as the x-mark in the profilecurve H of FIG. 11A, the point MN can be used as the measurementposition of the lens meter.

In contrast, in the case where the opening diameter of the lens meter issmaller than the pupil diameter, as shown in FIG. 12A, the measurementposition MN can be displaced from the point ON toward the nose side. InFIG. 12A, like components are denoted by like reference numerals as ofthose of FIG. 11A, and the explanation thereof will be omitted. In otherwords, as shown in FIG. 12B, in the case where the opening diameter D ofthe lens meter is smaller than the pupil diameter E, the peak value Pmnof the averaged distribution obtained by averaging the refractive powerdistribution of the progressive addition lens Q within the area of theopening diameter D is greater than the peak value Pvn of the averageddistribution obtained by averaging the refractive power distribution ofthe progressive addition lens Q within the area of the pupil diameter E,and therefore the position of the peak value Pmn is displaced toward thenose side. In such a case, as shown in FIG. 12A, the measurement can beperformed at the point MN, which is displaced from the point ON towardthe nose side.

As described with reference to FIGS. 10A to 12B, either in the casewhere the design principal meridian curve M and the principal line ofvision L of the progressive addition lens are the same or in the casewhere the design principal meridian curve M and the principal line ofvision L of the progressive addition lens are displaced from each other,by defining the peak position of the average power distribution or thepeak position of the astigmatism distribution averaged within theopening diameter D of the lens meter as the inspection position wherethe amount of inward movement is to be inspected by the lens meter, itcan be evaluated that the processing of the lens is performed inaccordance with design if the amount of inward movement obtained basedon the measured value at the inspection position becomes the presetamount of inward movement at the corrected inspection position.

Further, although the corrected position is used as the inspectionposition for inspecting the amount of inward movement in the aforesaidmethod, there is alternatively another method in which the measurementposition is not corrected, but instead the inspected value is correctedand then the evaluation is performed based on the corrected inspectedvalue.

In such a case, if the lens is the progressive addition lens Q shown inFIG. 11A, for example, the measurement is performed at the point ON ofFIG. 11B. Here the target value of the measurement is not Pvn, but is avalue obtained correcting value of the curve indicated by the dashedline, which is a curve averaged within the opening diameter D. So thatthe target value is corrected in such a manner, and if a value withinthe threshold is measured from the corrected target value, the amount ofinward movement OI can be obtained, then it can be evaluated that theprocessing of the lens is performed in accordance with design.

Note that, as shown in FIGS. 12A and 13A, the shift amount MH of thepoint MN (the measurement position) from the point ON or point DN variesdepending on the ratio of the size of the opening diameter D to the sizeof the pupil diameter E, the distribution state of average power orastigmatism, the power, and the like. Incidentally, in the case wherethe size of the opening diameter D of the lens meter and the size of thepupil diameter E of the wearer are the same (for example, both are 6mm), the measurement position can be the point ON (=VN).

Further, the calculation method of the averaging procedure within theopening diameter D of the lens meter is not particularly limited but canalso be the specific averaging method owned by each device. Further, thepresent invention can be applied to a progressive addition lens whoserefractive power changes on its front surface, a progressive additionlens whose refractive power changes on its rear surface, and aprogressive addition lens whose refractive power changes on its bothsurfaces.

Furthermore, unless there is a specific reason, it is not necessary toconsider the average value within the pupil diameter and the averagevalue within the opening diameter in the case where the distribution ofthe average power and the distribution of the astigmatism are averagelydesigned instead of being asymmetrical with the principal meridian curveas a boundary, or in the case where, although the distribution of theaverage power and the distribution of the astigmatism are asymmetrical,the density of the distributions almost do not change.

FIG. 13 is a flowchart for explaining the production process of theprogressive addition lens including the evaluation step by theevaluation method of the progressive addition lens according to theaforesaid embodiment of the present invention. First, in the process ofproducing, the optical characteristics (such as power, refractive powerdistribution state, layout position and the like) of the progressiveaddition lens is designed (Step S11), and the lens is trial-producedaccording to the design (Step S12). Further, in the process of verifyingwhether or not the trial-produced lens is produced according to thedesign, the lens meter is placed at the measurement position which isdetermined taking into consideration of the opening diameter of the lensmeter (i.e., the point MN shown in FIGS. 10A to 12B, which is thecorrected measurement position) to measure the amount of inward movement(Step S13). The amount of inward movement is obtained based on the powermeasured at the point MN, and it is judged whether or not the amount ofinward movement is within the threshold (Step S14). Further, if theamount of inward movement obtained based on the measurement is notwithin the threshold (“NO” in Step S14), then it is judged whether ornot reprocessing should be done (for example, whether or notreprocessing is possible) (Step S15), and if it is judged thatreprocessing should not be done (“NO” in Step S15), then the productionis completed. If it is judged that reprocessing should be done (“YES” inStep S15), then the details of reprocessing (the places to be processedand the amount of processing) are outputted to the processing machine(Step S16) to perform reprocessing (Step S12). The aforesaid steps areperformed repeatedly, and the production is completed until it is judgedin Step S14 that the amount of inward movement is within the threshold(“YES” in Step S14).

By the aforesaid steps, it is possible to suppress the influence of theopening diameter of the lens meter (i.e., to suppress the influencecaused by the error of the measuring device) to therefore accuratelymeasure the amount of inward movement of the progressive addition lens,so that it is possible to more suitably evaluate the progressiveaddition lens.

Note that, although the design method of the progressive addition lens,the asymmetrical progressive addition lens designed using the designmethod, and the evaluation method for evaluating progressive-power aredescribed above as the embodiments and examples of the presentinvention, it should be understood that the present invention is notlimited to the aforesaid embodiments and examples, but includes variousmodifications and variations without departing from the spirit of thepresent invention described in the claims.

EXPLANATION OF REFERENCE NUMERALS

-   L principal line of vision-   F position of front distance vision-   ON position of front near vision-   M design principal meridian curve-   DN position of near vision in design principal meridian curve-   H profile curve in horizontal direction-   OI amount of inward movement of line-of-sight-   DH amount of design inward movement-   MN measurement position after correction-   MH amount of inward movement for measurement

The invention claimed is:
 1. A method for inspecting a progressiveaddition lens in a process of manufacturing the same, the lens designedso that at least one of an average power distribution and an astigmatismdistribution is bilaterally asymmetrical in the horizontal directionwith a design principal meridian curve as a boundary, the methodcomprising: taking into consideration of an error caused by smoothingthe average power distribution or the astigmatism distribution within ameasurement range of a lens meter between an amount of inward movement,as a target value, at a position corresponding to a front near visionand an inspected value of the lens meter, correcting an error of aninspection position where the amount of inward movement is to beinspected by the lens meter, and evaluating the amount of inwardmovement at the corrected inspection position.
 2. The method forinspecting the progressive addition lens according to claim 1, whereineither one of a peak position of the average power distribution smoothedwithin the measurement range of the lens meter and a peak position ofthe astigmatism distribution smoothed within the measurement range ofthe lens meter is selected as the corrected inspection position.
 3. Themethod for evaluating the progressive addition lens according to claim1, comprising: setting an amount of inward movement MH of themeasurement position and an amount of inward movement of line-of-sightOI, wherein an expressionMH<OI is satisfied in a case where a pupil diameter E is greater than anopening diameter of the lens meter, an expressionMH=OI is satisfied in a case where the pupil diameter E is equal to theopening diameter of the lens meter, and an expressionMH>OI is satisfied in a case where the pupil diameter E is equal to theopening diameter of the lens meter, when: an intersecting line of aline-of-sight of a wearer of the progressive addition lens from adistance vision to a near vision and a refractive surface of theprogressive addition lens is defined as a principal line of vision L; inthe principal line of vision, a position corresponding to a frontdistance vision and a position corresponding to the front near vision ofthe wearer of the progressive addition lens are respectively defined asa point F and a point ON; a displacement of the point ON from the pointF toward the nose side in the horizontal direction is defined as anamount of inward movement of line-of-sight OI; an intersection of aprofile curve in horizontal direction H and the design principalmeridian curve M on the refractive surface of the progressive additionlens is defined as a point DN, in which the profile curve in horizontaldirection H passes through the point ON in the principal line of vision,and the design principal meridian curve M passes through the point F ofthe front distance vision and has an interval where the powerprogressively changes from an upper portion toward a lower portion ofthe progressive addition lens; a displacement of the point DN of thedesign principal meridian curve M from the point F of the front distancevision toward the nose side in the horizontal direction is defined as anamount of design inward movement DH; a position in the profile curve inhorizontal direction H at which a smoothed distribution reaches themaximum value is defined as a point VN, in which the smootheddistribution is calculated by smoothing the average power distributionor the astigmatism distribution along the profile curve in horizontaldirection H, which passes through the point ON, within a range of thepupil diameter E of the wearer of the progressive addition lens; theprogressive addition lens is designed by selecting the amount of designinward movement DH so that a displacement VH of the point VN from thepoint F toward the nose side in the horizontal direction becomes closeto the amount of inward movement of line-of-sight OI; the measurementposition of the lens meter for measuring the amount of inward movementof the progressive addition lens is defined as a point MN in the profilecurve in horizontal direction H; and a displacement of the point MN fromthe point F of the front distance vision toward the nose side in thehorizontal direction is defined as an amount of inward movement MH ofthe measurement position.
 4. The method for inspecting the progressiveaddition lens according to claim 1, wherein the method is performedafter processing of the lens in the process of manufacturing the lens.5. The method for inspecting the progressive addition lens according toclaim 1, wherein the method is performed in designing the lens afterprocessing of the lens in the process of manufacturing the lens.
 6. Amethod for inspecting a progressive addition lens in a process ofmanufacturing the same, the lens designed so that at least one of anaverage power distribution and an astigmatism distribution isbilaterally asymmetrical in the horizontal direction with a designprincipal meridian curve as a boundary, the method comprising: takinginto consideration of an error caused by smoothing the average powerdistribution or the astigmatism distribution within a measurement rangeof a lens meter between an amount of inward movement, as a target value,at a position corresponding to a front near vision and an inspectedvalue of the amount of inward movement obtained by the lens meter,correcting an error of the inspected value of the amount of inwardmovement obtained by the lens meter, and evaluating the amount of inwardmovement based on the corrected inspected value.
 7. The method forinspecting the progressive addition lens according to claim 6, whereinthe method is performed after processing of the lens in the process ofmanufacturing the lens.
 8. The method for inspecting the progressiveaddition lens according to claim 6, wherein the method is performed indesigning the lens after processing of the lens in the process ofmanufacturing the lens.